Four-component objective having two movable components



SEARCH ROOM Sept. 27, 1966 K. H. MAcHl-:R 3,274,887

FOUR-COMPONENT OBJECTIVE HAVING TWO MOVABLE COMPONENTS Filed Jan. 16,1963 MWMMMMM; Id u liw mi w .nl ,.m li L .m .m m il- W Vi i .U lillatx.. i|.|li1,|t null? mu/fe Allin u r KARL H. MACHER Inventor.'

United States Patent 2 claims. (l. sis- 51) My present invention relatesto a varifocal objective of the type wherein two movable components ofnegative refractivity are disposed between two fixed components ofpositive refractivity to form a system of invariable backfocal length,and therefore of fixed image plane, which can be adjusted between aminimum overall focal length fmm and a maximum overall focal lengthfmax.

The general object of .this invention is to provide a high-speedobjective of the aforedescribed type which consists of a relativelysmall number of lenses including a front lens of moderate dimensions,has a large relative aperture with little residual aberration throughoutits range of adjustment, and affords uniform illumination of the entireimage field even with small diaphragm stops short-range focusing.

This object is realized, in accordance with the instant invention, bythe provision of an objective system of the general character set forthabove wherein the image-side positive component (i.e. the fixed rearcomponent located on the side of the shorter light rays) consists of aplurality of air-spaced lens members-preferably four-of which the firstand the last one are biconvex lenses with external surfaces whose radiiof curvature have ratios bearing a predetermined relationship with eachother. More particularly, the ratio of the absolute values of the outer(rear) and inner (front) radii of the last lens member should be of thesame order of magnitude as the ratio of the absolute magnitudes of theouter (front) and inner (rear) radii of the first lens member of thiscomponent, i.e. should range between substantially 0.7 and 1.3 times thelatter ratio. Also, the ratio of the absolute values of the radii of therear and front surfaces of the positive first component should be lessthan the absolute ratio fI/fmm where f1 is the individual focal lengthof this first component. Furthermore, the two movable components areconstituted by negatively refracting lenses (preferably singlets) withfacing concave surfaces, the radius of the concave surface of the secondcomponent having an absolute value greater than that of the radius ofthe confronting concave surface ofthe vthird component.

For a satisfactory correction of chromatic aberrations, i.e. suppressionof color halos and maintenance of contrasts, I prefer to design thepositive first component as a biconvex doublet with a dispersiveinternal cemented surface whose radius of curvature has an absolutevalue smaller than that of the radius of its external front surface. Forthe same purpose it is desirable to construct the first lens member ofthe positive rear component (i.e. the fifth lens of the system if thefront component is a doublet and the two negative components aresinglets) as a positive singlet with an Abb number v 60.0.

In order to realize a very compact construction, with a short totalaxial length and correspondingly reduced front-lens diameter, a furtherfeature of the invention resides in such a dimensioning of the spacingof the two fixed components that the three variable air spaces separat-Patented Sept. 27, 1966 ICC ing the two variable components from thesefixed components and from each other add up to a value which is at mostequal to of the absolute value of the individual focal length fn of thesecond component, i.e. of the more forwardly positioned movablecomponent.

In the sole figure of the accompanying drawing I have showndiagrammatically an objective system representing a preferred embodimentof the invention.

The system illustrated inthe drawing consists of a total of eight lensesL1 to L8 constituting four components I, II, III and IV. The fixedcomponent I is a positive doublet consisting of biconvex lens L1 (radiir1, r2 and thickness d1) cemented onto lens L2 (radii r2, r3 andthickness d2) having the shape of a negative meniscus; the internalsurface r2 of this component is negatively refracting since therefractive index of lens L2 is higher than that of lens L1. A variableair space d3 separates the doublet L1/L2 from the second component IIwhich is a nearly planoconcave negative singlet L3 with radii r4, rS andthickness d4. The concave surface r5 of lens L3 confronts, across avariable air space d5, a concave surface of smaller radius r6 of themeniscus-shaped negative lens L4 which constitutes the third componentIII and whose thickness and second radius have been designated d6, f7. Afurther variable air space d7 separates lens L4 from the first lensmember L5 of fixed rear component IV which is a biconvex singlet havingradii f8, r9 and thick-ness d8; the other members of this component area biconvex singlet L6 (radii r10, r11 and thickness d10), a biconcavesinglet L7 (radii r12, r13 and thickness d12) and a biconvex singlet L8(radii r14, r15 and thickness d14), the intervening air spaces havingbeen indicated at d9, dll and d13.

The following Table A lists representative values for the parameters r1to r15 and d1 to d14 of lenses L1 to L8, their refractive indices nd andtheir Abb numbers v. The system has a relative aperture of 1:1.8 and afocal length ranging between 50 and 150 units of length (e.g.millimeters), the radii, thicknesses and separations being given in thesame linear units.

Table A nd v r1 =+290.98 L1 d1 =42.50 1. 61772 49. 78 I r2 =2l6.32

d3 =115.36 Variable air space r4 =-7550.72 II L3 d4 :10.00 1. 62041 60.29

d5 =39.35 Variable a r space r6 =88.75 III L4 d6 =5.00 1. 62041 60. 29

d7 =27.80 Variable nir space 18 =+260.02 L5 d8 =l0.00 1. 52310 50. 03

d9 =15.00 Air sp ce r10= +5080 L6 d10= 12.50 l. 74400 44. 90

r11 -575.75 IV d11=12.00 Air sp co rl2= -78.31 L7 d12= 13.75 1. 7408028. 05

d13=4.00 Air sp ce r14= +4203 L8 dl4= 15.00 1. 67790 55.52

dzaal=329.76

As will be noted from the foregoing Table A, the outer and inner radiir15, r14 of the last lens L8 of rear component IV have a ratio whoseabsolute value (1.42) lies between 0.7 and 1.3 times, i.e. 1.06 and1.96, of the absolute value (1.51) of the ratio of the outer and innerradii r8, r9 of the rst lens L5 of this component. The ratio of theexternal radii r3 and r1 of front lens L1 has an absolute value of 2.61which is less than the absolute quotient (8.12) of the individual focallength f1=406.1 of this front lens divided by the minimum focal lengthfmm=50 of the overall system. It will further be seen that the internalradius r2 of component I, i.e. lens L1, has an absolute value less thanthat of the radius r1 of its front surface and that the three variableair spaces d3, d and d7 add up to a length of 182.51 which is less than120% of the absolute value (192.18) of the individual focal lengthfn=160.15 of the first movable component II. The Abb number v of the rstlens L5 of rear component IV is less than 60.

The values for air spaces d3, d5 and d7 given in Table A are for anintermediate overall focal length f=100. The following Table B liststheir values for different positions of adjustment:

Table B d3 d5 d7 f e. 114. oo 31. e4 5o 115. as a9. 35 21. so 10o 164.59 11. 46 6. 45 150 I claim:

1. An optical objective comprising a biconvex doublet L7, L2constituting a fixed positive first component I, a lens L3 constitutinga negative second component II, a lens L4 constituting a negative thirdcomponent III, and a fixed positive fourth component IV consisting of aplurality of air-spaced lens members L5, L6, L7, L8; said second andthird components being movable, relatively to each other and to saidfirst and fourth components, into a first position in which theobjective has a relatively small focal length, a second position inwhich the objective has an intermediate focal length, and a thirdposition in which the objective has a' relatively large focal length;said lenses L1 to L8 having radii of curvature r1 to r15 and thicknessesand separations d1 to d14 whose numerical values, based upon a value of100 units for an intermediate overall focal length, together with theirrefractive indices nd and 4 Abb numbers if are substantially as given inthe following table, with the spacings d3, d5 and d7 given for saidsecond position:

nd v

r1 =-i290.93 L1 d1 =42.50 1.01772 40. 78 I r2 =21G.32

L2 d2 :7.50 1. 75520 27. 53 r3 =-7G0.07

d3 =1l5.36 Air space r4 =-7550.72 II L3 d4 =10.00 1.62011 GO. 20

d5 =39.35 Air sp ce r6 88.75 III L4 d6 =5.00 1. 62041 00. 29

d7 :27.80 Air spA ce f8 =+260.02 L5 d8 =10.00 l. 52310 50. 93

di) =15.00 Air space r10=+50.80 L6 dl0=12.50 1.74400 44. 90

r11=575.75 IV d11=12.00 Air sp ice rl2=78.31 L7 dl2=13.75 1. T4080 28.05

d13=4.00 Air space r14=|42.03 L8 dl4=15.00 1. 67790 55. 52

dtotnl=329.76

2. An objective as dened in claim 1 wherein said spaces d3, d5 and d7have substantially the following values in said first and thirdpositions:

d3 d5 (i7 First position 6. 86 144. 00 31.64 Third position 164. 59 11.6. 45

References Cited by the Examiner UNITED STATES PATENTS JEWELL H.PEDERSEN, Primary Examiner.

JOHN K. CORBIN, Examiner.

1. AN OPTICAL OBJECTIVE COMPRISING A BICONVEX DOUBLET L7, L2 CONSTITUTING A FIXED POSITIVE FIRST COMPONENT I, A LENS L3 CONSTITUTING A NEGATIVE SECOND COMPONENT II, A LENS L4 CONSTITUTING A NEGATIVE THIRD COMPONENT III, AND A FIXED POSITIVE FOURTH COMPONENT IV CONSISTING OF A PLURALITY OF AIR-SPACED LENS MEMBERS L5, L6, L7, L8; SAID SECOND AND THIRD COMPONENTS BEING MOVABLE, RELATIVELY TO EACH OTHER AND TO SAID FIRST AND FOURTH COMPONENTS, INTO A FIRST POSITION IN WHICH THE OBJECTIVE HAS A RELATIVELY SMALL FOCAL LENGTH, A SECOND POSITION IN WHICH THE OBJECTIVE HAS AN INTERMEDIATE FOCAL LENGTH, AND A THRID POSITION IN WHICH THE OBJECTIVE HAS A RELATIVELY LARGE FOCAL LENGTH; SAID LENSES L1 TO L8 HAVING RADII OF CURVATURE R1 TO R15 AND THICKNESSES AND SEPARATIONS D1 TO D14 WHOSE NUMERICAL VALUES, BASED UPON A VALUE OF 100 UNITS FOR AN INTERMEDIATE OVERALL FOCAL LENGTH, TOGETHER WITH THEIR REFRACTIVE INIDICES ND AND ABBE NUMBERS V ARE SUBSTANTIALLY AS GIVEN IN THE FOLLOWING TABLE, WITH THE SPACINGS D3, D5 AND D7 GIVEN FOR SAID SECOND POSITION: 